How to Cache OG Images

Caching OG images means serving a previously-generated social preview from a CDN instead of re-rendering it on every share. FastOG caches identical images at the edge for a year — the same URL returns the cached PNG in 0 credits and at roughly zero latency, so most of a site's OG traffic never touches the renderer.

Why caching matters

A social share triggers a fetch by the platform's crawler. If every share re-rendered, you would burn credits and latency on identical content. Aggressive caching — keyed on the image's content — turns "every share costs 1 render" into "the first share costs 1 render, every other share is free."

The content-keyed model that makes it work

FastOG uses content-signed URLs: the URL is a pure function of the parameters. Identical title + template → identical URL. That means:

The CDN caches on the URL.
Same content shared 10,000 times → one render, one credit, 9,999 cache hits.
Change the content → different URL → one new render.

GET /api/v1/og?title=Hello&template=default&key=...&s=...   → render (1 credit), then
GET /api/v1/og?title=Hello&template=default&key=...&s=...   → cached (0 credits, instant)
GET /api/v1/og?title=Changed&template=default&key=...&s=... → render (1 credit)

FastOG's caching headers

FastOG returns Cache-Control: public, max-age=31536000, immutable (one year) for rendered images, and Cloudflare caches the result. Subsequent fetches return cf-cache-status: HIT.

Caching your own og:image (self-hosted)

If you store images yourself instead of using FastOG's cache, apply the same rules:

Step	Detail
Cache key = content hash	Store by a hash of the data, not a mutable filename
Long TTL	`max-age=31536000, immutable` for stable content
Versioned URLs	Append a hash/version when content changes
CDN in front	Let the CDN absorb repeat fetches

FAQ

Do repeat shares really cost 0 credits?

Yes. Identical URLs hit the edge cache and never reach the renderer — no credit is consumed.

How long does FastOG cache an image?

One year (immutable). Long after first render, a shared card is served from cache.

What if I want an image to update (e.g. live price)?

Change a parameter (the price) → new URL → new render. Stable content stays cached; dynamic content updates when you want it to.

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